In a typical pin tumbler lockset—also known as a cylinder lock—there is a cylinder plug mounted for rotation within a housing. When the cylinder plug is rotated, it actuates a lockset mechanism to pull in a latch or activate a deadbolt function to lock or unlock the door. The movement of the lockset mechanism is based on the rotation of a properly bitted key inserted into a keyway in the cylinder plug, and a cam or tailpiece is attached to the cylinder plug and is coupled to the lockset mechanism. Twisting the key rotates the plug, thereby turning the cam or tailpiece and actuating the locket mechanism.
Mechanically keyed cylinders require that the cylinder plug be returned to the home, or “locked,” position in order to remove the key. This is due to the fact that the key is captured by the pin tumblers of the cylinder until the cylinder plug is rotated back to the home position and the pin tumblers can disengage the key, thereby permitting the key to be removed from the keyway. Thus, after opening the lock, the user must rotate the key back to the locked position before he can withdraw his key from the lock. This ensures that the cylinder plug, and any cam or tailpiece attached to the plug, is positioned back in the home or “locked” position as well. Typically, the cam or tailpiece is rotated away from the lockset mechanism and is in a position out of the way of any of the lockset drive mechanism when the cylinder plug is in the locked rotational position. For one-way doors, such as emergency exit doors that are locked from the outside but are unlocked from the inside in case emergency exit through the door is required, moving the cam or tailpiece away from the lockset mechanism ensures that the cam or tailpiece will not interfere with the lockset in any manner that may affect the ability to actuate the lockset and open the door from inside.
Certain electronic variations of the cylinder lock have a thumb turn or “knob” coupled to the lockset—e.g., via a “plug”—and do not include pin tumblers or do not employ a mechanical key to actuate the cylinder/lockset mechanism. An electronically-controlled (e.g., by an electric motor or solenoid) blocking element is configured to selectively block or permit rotation of the knob and the cylinder plug. In the locked condition, the blocking element is configured in a state that blocks rotation of the knob and the cylinder plug. When a valid credential, which may, for example, comprise an RFID tag, is presented by the user to a reader of the electronic lock, the state of the blocking element is electronically altered to an unlocked condition that permits rotation of the knob. With the blocking element in the unlocked condition, the user can rotate the knob which is coupled to the cam or tailpiece through the plug (as is in the mechanical cylinder lock) and operate the lockset mechanism. In this example, there is no key captured within the lock which requires that the user return the cylinder plug back to the home, or locked, position so that the key can be removed. Nevertheless, it is necessary for the user to manually return the knob attached to the cylinder plug back to the home position in order to relock the cylinder plug and move the cam back to the home position to disengage the lockset mechanism. If the knob is not returned to the locked position, for example, if the user simply forgets to return the knob to the locked position, the cylinder plug will remain in the unlocked condition, thereby cause a security lapse. In addition, the cam or tail piece will not be returned to a home position and may be left stranded in a position engaged with the lockset. This could interfere with operation of the lockset. For example, for doors that are locked on one side and opened on the opposite side, interference with the lock set could prevent opening of the door from the opened side.
Relying on the user to remember to manually return the cylinder plug to the locked, home position to ensure that the cylinder lock is relocked or to ensure that the cam attached to the plug is returned to the home position, is not ideal.
Thus, there is a need in cylinder locks that must be returned to the home, or locked, position to provide an automatic return feature that automatically returns the cylinder plug to the home position.